Control of cooperative switching of microwrinkle orientations by nanopatterns.

ABSTRACT

Microwrinkles are mechanically self-organized surface undulations with an intrinsic wavelength lambda(0) showing various stripe patterns. The average orientation of the stripes is repeatedly altered by changing, for example, the direction of uniaxial compression applied to the sample. Meanwhile, the stripe patterns can be modulated arbitrarily by the designed topographic patterns through mechanical coupling. Exploiting these results, here we study the switching of the microwrinkle orientations, that is, stripe patterns, under the influence of the artificial nanopatterns with a characteristic periodicity d. The switching is primarily driven by the rotation of the compression axis. The nanopattern-induced boundary condition disturbs the formation of the optimal stripe pattern having lambda(0). Thus a variety of modulated stripe patterns appear depending on both the relative value, lambda(0)/d (0.5-1.6), and the direction of the uniaxial compression. The relative length, lambda(0)/d, also affects the transition of the stripe patterns, showing different dynamics of the domain walls characterized by their creation, annihilation, and configurations. This results correlate with hysteresis of the spatially averaged stripe orientation for a rotation cycle of the compression direction. The results suggest for the general self-organized stripe patterns that we can tune the transition of the stripe pattern, in other words, the cooperative response of the coupled local stripe orientations, as well as the stripe patterns themselves, by exploiting the artificial patterns with proper designs.